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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Wide-Field Imaging of Galactic Halos with a Near-Infrared Rocket-Borne Telescope

We successfully completed both of the proposed flights by May of 1998, on schedule and on budget. In both flights the instrument worked flawlessly, achieving sensitivities slightly better than the specification (1 nW/sq m sr per pixel). The payload was recovered with only minor damage after both flights. The results from the first flight, which targeted the nearby edge-on spiral NCG 4565, have been published. Analysis of the data failed to detect any significant emission, from the halo around the galaxy, and set a very stringent 2 sigma lower limit on the M/L ratio of the halo of greater than 260 in solar units. The results from the second flight, which targeted the infamous NGC 5907, have taken longer to analyze because of an offset in the absolute pointing of the payload which broke the symmetry of the scan pattern about the galaxy, thus complicating the analysis, After careful analysis, Caltech graduate student, Sarah Yost, has recovered the full sensitivity of the experiment, setting a 2 sigma lower limit on the M/L ratio of the halo of greater than 280 in solar units. This result rules out the hypothesis that a significant portion of the halo around NGC 5907 is composed of low-mass stars, as previous observations had suggested. NITE probes directly the halo at 10 to 30 kpc from the disk, a region far too dim for other experiments. Our conclusion is that observations of a significant IR signature associated with the halo at less than approximately 5kpc radius where contaminated by tidally disrupted disk population of stars. In order to test the idea that we could study faint surface-brightness fluctuations in the diffuse background using NITE, we have analyzed the data from the 1997 flight which targeted NCG 4565 (this target is in a region of lower stellar confusion than is NGC 5907). We have detected a significant correlation in the noise at zero-lag, with an amplitude that corresponds to brightness fluctuations of 3.04 plus or minus 0.16 nW/sq m sr. This work will be submitted for publication later this year. An important accomplishment of our sub-orbital program is the training graduate students and postdocs who will become future leaders in NASA's space astrophysics program. The PI has mentored 7 scientists that now hold tenure-track faculty positions or the equivalent at NASA research centers.

Lange, Andrew E.↗
NASA NTRS2001

Far-Infrared Extragalactic Surveys: Past, Present, and Future

As much as one third of the luminosity of the local universe is emitted in the far infrared. In order to understand the history of energy release in the universe, it is crucial to characterize this rest-frame far-infrared contribution from the present back to the era of initial galaxy formation. Over the redshift range from 0 to 10, this energy is received in the 80 micrometers to 1 mm spectral region. In the 1980's the Infrared Astronomy Satellite (IRAS) all-sky survey provided the first comprehensive view of the far infrared emission from the local universe. The diffuse background measurements by Cosmic Background Explorer Satellite (COBE) have provided constraints on the integral contributions from the high redshift universe. In the past five years, submillimeter measurements made using the SCUBA instrument have revealed powerful high redshift sources. To develop a clear history of energy release in the universe, we need numbers and redshifts of representative populations of energetically important objects. The near future will bring the Space Infrared Telescope Facility Multiband Imaging Photometer (SIRTF)(MIPS) survey, which will cover about 100 square degrees at wavelengths out to 160 micrometers, providing a large sample of energetically important galaxies out to z of approx.3. In 2005, the Japanese IRIS survey will provide a 160 micrometers full sky survey, which will provide larger samples of the high z galaxy populations and will find intrinsically rare high luminosity objects. The SPIRE instrument on the FIRST facility will extend these surveys to longer wavelengths, providing a view of the universe at higher redshifts in three spectral bands. A concept for an all-sky submillimeter survey is under development, called the Survey of Infrared Cosmic Evolution (SIRCE). With a 2 m cryogenic telescope, it can map the entire sky to the confusion limit in the 100 to 500 micrometers range in six months. This survey will provide photometric redshifts, number counts, and will find the most luminous objects in the universe. In the next decade, the opening of the submillimeter, combined with the near infrared capability of NGST will provide us with a clear picture of energy release in the early universe.

Moseley, Samuel H., Jr.↗
NASA NTRS2003

Stacking Searches for Greater Than 100 MeV Gamma Ray Emission from Radio Galaxies and Seyfert Galaxies

The EGRET telescope on CGRO detected more than sixty sources of high-energy gamma radiation associated with active galactic nuclei (AGN). All but one of those belong to the blazar subclass; the only exception is the nearby radio galaxy Centaurus A. Since there is no obvious reason other than proximity to expect Cen A to be the only non-blazar AGN emitting in high-energy gamma rays, we have utilized the "stacking" technique to search for $>100$-MeV emission from two non-blazar AGN subclasses, radio galaxies and Seyfert galaxies. Maps of gamma-ray counts, exposure, and diffuse background have been created, then co-added in varying numbers based on sorts by redshift, 5-GHZ flux density, and optical brightness, and finally tested for gamma-ray emission. No detection significance greater than $2\sigma$ has been found for any subclass, sorting parameter, or number of objects co-added. Monte Carlo simulations have also been performed, to validate the technique and estimate the significance of the results.

Cillis, A. N.↗
NASA NTRS2004

Research on the Natural Variability of Climate

The scheme for ocean vertical mixing presented in Canuto, Howard, Cheng & Dubovikov and Canuto, Howard, Hogan, Cheng, Dubovikov & Montenegro [GISS mixing scheme] was extended to include the latitudinal dependence reported by Gregg, Sanford & Winkel of the input to the interior ocean turbulence field of energy from internal waves. The resulting latitude dependence was implemented in our module of code for the GISS vertical mixing scheme and tested in the global NCAR-CSM ocean model with 3 degree X 3 degree resolution and 25 levels in the vertical. With the latitude dependence, the background diffusivity decreases from approx. 0.1 sq cm/sec at midlatitudes to approx. less than 0.01 sq cm/sec at the equator. A significant improvement was seen in the tropical ocean, with tropical thermoclines being sharpened in agreement with the requirements of observational studies and the needs of ENS0 modeling. At the same time global measures nf performance such as the meridional overturning and northward heat transport were not adversely affected. Results were presented at the 2004 Layered Ocean Modeling meeting and a paper has been prepared and submitted to Geophysical Research Letters.

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NASA NTRS1991

Gamma Ray Observatory (GRO) Prelaunch Mission Operations Report (MOR)

The NASA Astrophysics Program is an endeavor to understand the origin and fate of the universe, to understand the birth and evolution of the large variety of objects in the universe, from the most benign to the most violent, and to probe the fundamental laws of physics by examining their behavior under extreme physical conditions. These goals are pursued by means of observations across the entire electromagnetic spectrum, and through theoretical interpretation of radiations and fields associated with astrophysical systems. Astrophysics orbital flight programs are structured under one of two operational objectives: (1) the establishment of long duration Great Observatories for viewing the universe in four major wavelength regions of the electromagnetic spectrum (radio/infrared/submillimeter, visible/ultraviolet, X-ray, and gamma ray), and (2) obtaining crucial bridging and supporting measurements via missions with directed objectives of intermediate or small scope conducted within the Explorer and Spacelab programs. Under (1) in this context, the Gamma Ray Observatory (GRO) is one of NASA's four Great Observatories. The other three are the Hubble Space Telescope (HST) for the visible and ultraviolet portion of the spectrum, the Advanced X-ray Astrophysics Facility (AXAF) for the X-ray band, and the Space Infrared Telescope Facility (SIRTF) for infrared wavelengths. GRO's specific mission is to study the sources and astrophysical processes that produce the highest energy electromagnetic radiation from the cosmos. The fundamental physical processes that are known to produce gamma radiation in the universe include nuclear reactions, electron bremsstrahlung, matter-antimatter annihilation, elementary particle production and decay, Compton scattering, synchrotron radiation. GRO will address a variety of questions relevant to understanding the universe, such as: the formation of the elements; the structure and dynamics of the Galaxy; the nature of pulsars; the existence of black holes; the possible existence of large amounts of antimatter, energetic and explosive phenomena occurring in galactic nuclei; the origin of the cosmic diffuse background; particle acceleration in the Sun, stars and stellar systems; processes in supernovae; and the origin and evolution of the universe itself.

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NASA NTRS2006

Spatial Correlation Function of the Chandra Selected Active Galactic Nuclei

We present the spatial correlation function analysis of non-stellar X-ray point sources in the Chandra Large Area Synoptic X-ray Survey of Lockman Hole Northwest (CLASXS). Our 9 ACIS-I fields cover a contiguous solid angle of 0.4 deg(exp 2) and reach a depth of 3 x 10(exp -15) erg/square cm/s in the 2-8 keV band. We supplement our analysis with data from the Chandra Deep Field North (CDFN). The addition of this field allows better probe of the correlation function at small scales. A total of 233 and 252 sources with spectroscopic information are used in the study of the CLASXS and CDFN fields respectively. We calculate both redshift-space and projected correlation functions in co-moving coordinates, averaged over the redshift range of 0.1 < z < 3.0, for both CLASXS and CDFN fields for a standard cosmology with Omega(sub Lambda) = 0.73,Omega(sub M) = 0.27, and h = 0.71 (H(sub 0) = 100h km/s Mpc(exp -1). The correlation function for the CLASXS field over scales of 3 Mpc< s < 200 Mpc can be modeled as a power-law of the form xi(s) = (S/SO)(exp - gamma), with gamma = 1.6(sup +0.4 sub -0.3) and S(sub o) = 8.0(sup +.14 sub -1.5) Mpc. The redshift-space correlation function for CDFN on scales of 1 Mpc< s < 100 Mpc is found to have a similar correlation length so = 8.55(sup +0.74 sub -0.74) Mpc, but a shallower slope (gamma = 1.3 +/- 0.1). The real-space correlation functions derived from the projected correlation functions, are found to be tau(sub 0 = 8.1(sup +1.2 sub -2.2) Mpc, and gamma = 2.1 +/- 0.5 for the CLASXS field, and tau(sub 0) = 5.8(sup +.1.0 sub -1.5) Mpc, gamma = 1.38(sup +0.12 sub -0.14 for the CDFN field. By comparing the real- and redshift-space correlation functions in the combined CLASXS and CDFN samples, we are able to estimate the redshift distortion parameter Beta = 0.4 +/- 0.2 at an effective redshift z = 0.94. We compare the correlation functions for hard and soft spectra sources in the CLASXS field and find no significant difference between the two groups. We have also found that the correlation between X-ray luminosity and clustering amplitude is weak, which, however, is fully consistent with the expectation using the simplest relations between X-ray luminosity, black hole mass, and dark halo mass. We study the evolution of the AGN clustering by dividing the samples into 4 redshift bins over 0.1 Mpc< z <3.0 Mpc. We find a very mild evolution in the clustering amplitude, which show the same evolution trend found in optically selected quasars in the 2dF survey. We estimate the evolution of the bias, and find that the bias increases rapidly with redshift (b(z = 0.45) = 0.95 +/- 0.15 and b(z = 2.07) = 3.03 +/- 0.83): The typical mass of the dark matter halo derived from the bias estimates show little change with redshift. The average halo mass is found to be log (M(sub halo)/M(sun))approximates 12.1. Subject headings: cosmology: observations - large-scale structure of the universe - x-rays: diffuse background - galaxies: nuclei

Yang, Y.↗
NASA NTRS2011

Analysis of XMM-Newton Data from Extended Sources and the Diffuse X-Ray Background

Reduction of X-ray data from extended objects and the diffuse background is a complicated process that requires attention to the details of the instrumental response as well as an understanding of the multiple background components. We present methods and software that we have developed to reduce data from XMM-Newton EPIC imaging observations for both the MOS and PN instruments. The software has now been included in the Science Analysis System (SAS) package available through the XMM-Newton Science Operations Center (SOC).

Snowden, Steven↗
NASA NTRS1992

An upper limit on the cosmic ultraviolet background

The 1989 diffuse UV background data of Fix et al. (1989), when modeled as an optically thin, geometrically thin Galactic disk, implies an extragalactic UV background of 4 +/- 80 units at 0.15 micron, rather than the 530 +/- 80 units given by Fix et al. A more conservative fit allowing for forward scattering by dust and a finite optical depth to the Galactic pole gives a best-fit value of 45 units for the extragalactic flux, with a conservative limit of less than 500 units, similar to the lowest observed flux. Comparing the gradient of the UV flux versus csc absolute value of b with the IRAS 100 micron gradient implies an unexpectedly low scattering cross section for dust at 0.15 micron, compared to the absorption cross section in the visible.

Wright, Edward L.↗
NASA NTRS1992

CUBIC - A non-dispersive Diffuse X-ray Background spectrometer

The Cosmic Unresolved X-ray Background Instrument using CCDs (CUBIC) is designed to obtain spectral observations of the Diffuse X-ray Background (DXRB) with moderate spectral resolution over the energy range 0.2-10 keV, using mechanically-collimated CCDs. At this time, it is the only planned satellite payload devoted to the study of the spectrum of the DXRB. Over the anticipated 3 year lifetime of the satellite, CUBIC will be able to study up to 50 percent of the sky with 5 x 5 deg spatial resolution for the subkilovolt Galactic diffuse background, and with 10 x 10 deg spatial resolution for the extragalactic diffuse background above 2 keV. CUBIC will obtain high quality nondispersive spectra of soft X-ray emission from the interstellar medium, supernova remnants, and some bright sources, and will make a sensitive seach for line emission or other features in the extragalactic cosmic X-ray background from 2-10 keV.

Burrows, David N.↗
NASA NTRS1991

The evolution of the diffuse cosmic ultraviolet background constrained by the Hubble Space Telescope observations of 3C 273

Results are presented of recent HST UV spectroscopy of 3C 273, which revealed more low-redshift Lyman-alpha absorption lines (IGM clouds) than expected from the extrapolation from high-redshift (not less than 1.6) observations. It is shown on the basis of the standard pressure confined cloud model of the Lyman-alpha forest that this result indicates a sharp drop in the diffuse cosmic UV background from 2 to 0 redshift. It is predicted that the H I optical depth will drop slowly or perhaps even increase with decreasing redshift at less than 2 redshift. The implied constraints on the density and pressure of the diffuse IGM at 0 redshift are also derived. The inferred evolution of the diffuse UV flux bears a striking resemblance to the most recent direct determinations of the volume emissivity of the quasar population.

Ikeuchi, Satoru↗
NASA NTRS1986

A spectrometer to measure the diffuse, astronomical extreme ultraviolet background

The present grazing incidence spectrometer for measuring the diffuse astronomical background between 80 and 650 A uses a wire grid collimator to define a 40-arcmin by 15-deg field of view. After passing through the collimator, radiation impinges on an array of plane reflection gratings. An array of mirrors then focuses the diffracted light through a thin filter onto a microchannel plate detector. The resulting system focuses to a few arcmin and produces spectra with 10 to 20 A resolution. Performance characteristics of the spectrometer are discussed.

Labov, Simon↗
NASA NTRS1981

The diffuse extreme-ultraviolet background - Constraints on hot coronal plasma

The Apollo-Soyuz data and data reported by Cash et al. (1976) have been reanalyzed in terms of both isothermal models and temperature distribution models. In the latter case, a power-law form is assumed for the relation between emission measure and temperature. A new upper limit on diffuse flux in the 20-73 eV band derived from Apollo-Soyuz observations made in the earth's shadow has been incorporated in the calculation. In the considered investigation the results of the new analysis are presented and the implications for the physical properties of the hot component of the interstellar medium are discussed. The analysis of the Berkeley extreme ultraviolet (EUV) diffuse background measurements using either isothermal or power law temperature distribution models for the emitting plasma indicates excellent qualitative agreement with hard X-ray data that suggest the sun to be immersed in a hot plasma that pervades most of space out to approximately 100 pc.

Paresce, F.↗
NASA NTRS1988

Measurements of the anisotropy of the cosmic background radiation and diffuse galactic emission at millimeter and submillimeter wavelengths

The results of a balloon-borne observing program to measure the large angular scale brightness distribution of the 2.7 K cosmic background radiation (CBR) at millimeter and submillimeter wavelengths are reported. A new determination of the dipole anisotropy of the CBR is found with 3.40 + or - 0.42 mK toward alpha = 12.1 + or - 0.24 hr, delta = - 23 + or - 5 deg in a 1.2 to 8/cm band and 4.7 + or - 1.4 mK toward alpha = 9.9 + 1.7 or - 1.1 hr, delta = - 38 + or - 21 deg between 5 and 18/cm, where the amplitudes are listed as thermodynamic temperatures. New estimates of the absolute temperature in these two bands of 2.86 + or - 0.26 K and 3.01 + or - 0.31 are obtained under the assumption that the CBR has a Planck spectrum. The diffuse Galactic emission is fitted by a secant distribution in Galactic latitude, and the resulting Galactic pole antenna temperatures are given. Maps of sky brightness, measurements of zodiacal emission, and measurements of fluctuations of the atmospheric emission which dominates the noise budget are also presented.

Halpern, Mark↗
NASA NTRS1994

MACHOs and the diffuse X-ray background

The possible contribution of X-ray emission from massive compact objects in the Galactic halo (MACHOs) to the diffuse X-ray background is explored. We show that such emission cannot be responsible for the shadowing seen in soft X-ray observations by ROSAT but that these objects may indeed contribute significantly (at levels greater than 10%) to the diffuse background at higher (greater than or approximately 0.5 keV) energies. Thus, X-ray observations may well be able to significantly constrain the spatial distribution of MACHOs.

Kashyap, V.↗
NASA NTRS1983

Experimental limits of the extreme ultraviolet background

Photometric observations of the diffuse extreme ultraviolet background with two photometers having bandpasses of 750-940 A and 1040-1080 A are reported. The payload, which was flown aboard an ARIES sounding rocket in June 1982, is described, including the electron detectors, filters, and calibration. The operation of the probe during the experiment, including its motions, are described. The primary experiment involved spectroscopic observation of the hot white dwarf HZ43. The photometer count rate is shown and the measurements of the diffuse background are compared with theoretical predictions. Despite the lower limits obtained using a narrowband detector, the measurements are not sensitive enough to draw any relevant astrophysical conclusions.

Wulf-Mathies, C.↗
NASA NTRS2012

Resolving the Origin of the Diffuse Soft X-ray Background

In January 1993, the Diffuse X-ray Spectrometer (DXS) measured the first high-resolution spectrum of the diffuse soft X-ray background between 44-80A. A line-dominated spectrum characteristic of a 10(exp 6)K collisionally ionized plasma' was expected but while the observed spectrum was clearly line-dominated, no model would fit. Then in 2003 the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) launched and observed the diffuse extreme-ultraviolet (EUV) spectrum between 90- 265A. Although many emission lines were again expected; only Fe IX at 171.1A was detected. The discovery of X-rays from comets led to the realization that heavy ions (Z=6-28) in the solar wind will emit soft X-rays as the ions interact via charge exchange with neutral atoms in the heliosphere and geocorona. Using a new model for solar wind charge exchange (SWCX) emission, we show that the diffuse soft X-ray background can be understood as a combination of emission from charge exchange onto the slow and fast solar wind together with a more distant and diffuse hot (10(exp 6)K) plasma.

Smith, Randall K.↗
NASA NTRS1980

The diffuse gamma-ray background in the Hoyle-Narlikar cosmology

The paper analyzes the contributions of QSOs, BL-Lac objects and Seyfert galaxies to the diffuse gamma-ray background within the framework of the Hoyle-Narlikar theory. It is shown that the inconsistency reported in standard theory, namely that the evolutionary function needed to explain the gamma-ray data is very different from the one derived from the optical part of the spectrum, is no longer present. It is also shown that the contribution of a variable gravitational 'constant' to the expression for the diffuse background is the same as that of a density evolution function.

Canuto, V. M.↗
NASA NTRS1983

Origin of diffuse gamma-ray background

It is shown that the observed spectrum of the diffuse gamma-ray background could be accounted for by unresolved active galaxies even with no evolution, if their spectra are described by a spherical accretion/shock acceleration model (1983) and are steepened by photon-photon pair production interactions at high energies. The model is based on HEAO-1 and SAS-2 observations in the region of 2 to 165 keV and above 30 MeV. The model predicts a higher flux of high-energy neutrinos from active galaxies than models in which electrons are accelerated directly. It is noted that several active galaxies should be detectable by the Gamma-Ray Observatory, making it possible to determine the actual contribution of active galaxies to the diffuse gamma-ray background.

Protheroe, R. J.↗